Hot top panel insert unit



March 1969 w. M. CHARMAN, JR., ETAL 3 HOT TOP PANEL INSERT UNIT FiledOct. 7, 1966 MIXTURE OF EXPANDED CLAY SAND EXPANDED CLAY asA-0 so i 2 20g; g g

2 Q; INVENTORS g; g WALTER M. CHARMAN JR.

% $2 BY JAMES H. BORDEN We, u. s. MESH NO. ATTQRNEYW United StatesPatent 01 3,433,452" Patented Mar. 18, 1969 6 Claims ABSTRACT OF THEDISCLOSURE A panel insert unit for use in hot topping, said unit havinga front side and a rear side remote therefrom and comprising a pluralityof heat destructible panel sections having front faces for formingadjacent interior faces of a hot top opening, said panel sections havinga side edge surface facing each adjacent panel section, materialextending between and interconnecting said panel sections adjacent therear side of the unit and providing for relative angular movement ofsaid panel sections from an openedout shipping position where facingedge surfaces of adjacent panels sections are spaced to a position wherethe spaced edge surfaces of adjacent panels are in substantial contactto position the panels to form interior faces of the hot top and toblock leakage of molten metal between the panels.

This application is a continuation-in-part application of copendingUnited States application, Ser. No. 398,664, filed Sept. 23, 1964, nowabandoned.

The present invention relates to a refractory material for use in theconstruction of hot top structures and, more particularly, to arefractory panel forming a part of a hot top and which contacts themolten metal poured into the ingot with which the hot top is associated.

In hot topping operations, it is often necessary to manually orotherwise handle refractory hot top structures, such as refractorypanels. Depending upon the size of the ingot to be poured, the size ofthe hot top will vary and the size of the above-mentioned panels willlikewise vary. Because of the handling of these panels, it is desirableto construct the panels so that their weight is minimized. However, themechanical strength and thermal properties of the panels must meet therequirements for the particular use to which the panel is to be put.

In accordance with the present invention, refractory hot top panels aremade of a lightweight, highly insulating, expanded clay material. Theexpanded clay material is a granular aggregate made by a process inwhich clay pellets are bloated so as to create a porous particle. Thisgranular aggregate has a density of approximately 25-35 lbs. per

cu. ft. The density of raw clay, of course, varies depending upon itsparticle size, and is in the range of 65-90 lbs. per cu. ft. Moreover,the expanded clay material has a fusing temperature such that it retainsits cellular structure when used as a material in a hot top refractorypanel which contacts molten steel.

A further advantage of this expanded clay material is the structuralstrength of the expanded pellets. They can be shipped, stored, handled,and mulled in a muller with little or no degradation and loss ofcellular structure, as compared to other lightweight aggregatematerials, such as crushed-up insulating brick grog, which is relativelyfragile, and breaks up in handling as above.

This expanded clay aggregate clearly differs from other clay materials,having a density considerably less than a clay aggregate, raw orcalcined, which has been used as a material in a hot top structure asdisclosed in U.S. Patent No. 1,984,759. Calcined fire clay is slightlyless dense than raw fire clay and is not a substitute for the expandedclay aggregate of the present invention. Furthermore, the density ofcalcined fire clay is only slightly lighter than the raw clay.

The method of manufacturing the expanded clay is set forth in general inThe Ceramic Bulletin, 1964, vol. 43, issue No. 5, pp. 408-409. Ingeneral, the material is made by placing clean finely ground clay whichhas been brought to a paste consistency in a slinger head in a drier.The slinger head consists of a perforated band which revolves at some3,000 rpm. At this speed, centrifugal force hurls the paste throughholes in the outer rim of the slinger head which causes the paste to beformed into pellets. The pellets are dried in the drier. The driedpellets then flow through the firing chamber of a furnace whose wallsare at 2800-3000" E, where they are bloated and vitrified. The pelletsconsist of substantially porous cellular grains, and have refractoryproperties similar to those of the fire clay from which they wereformed.

In accordance with the present invention, the expanded clay material isused in the making of hot top structures, such as refractory panels, andspecifically is mixed with sand and a binder, giving the panels adensity within the range of 30-90 lbs. per cu. ft., depending on thesandexpanded clay ratio, and a modulus of rupture of at leastaproximately 250 lbs. per sq. in. or more. The panels are generally madeof a thickness of between 1 and 2". The panels have insulatingproperties of heat capacity and thermal conductivity (K factor)approximately equivalent to an insulating firebrick panel of theequivalent density and thickness.

The principal object of the present invention is the provision of a newnad improved lightweight hot top insulating refractory panel made of amaterial including expanded clay, sand, and a suitable binder in theproportion required to provide the panel with the proper mechanicalstrength, thermal properties and density.

Another object of the present invention is the provision of a new andimproved hot top panel which is relatively light in weight and has amultitude of small air pockets or spaces distributed throughout andwhich pockets are defined by porous grains of a cellular refractoryexpanded clay of which the panel is partially constructed.

A still further object of the present invention is the provision of anew and improved hot top panel made of a material including 15 to partsby weight of sand, 15 to 85 parts by weight of an expanded cellular claymaterial, and 3 to 20 parts by weight of a suitable binder.

Another object of the present invention is the provision of a new andimproved hot top insulating refractory panel made of a materialincluding expanded clay, sand, and a binder and having a density of 30-lbs. per cu. ft., a modulus of rupture of at least approximately 250lbs. per sq. in. and a thickness of between 1" and 2".

An additional object of the present invention is the provision of a newand improved hot top structure for use as the insulating lining of a hottop and comprising a plurality of preformed panels assembled to form anannular lining of a hot top, with the panels being interconnectd by aflexible material which maintains the panels in a predeterminedrelationship and which allows the panels and the flexible material to beassembled in a fiat position, to form a relatively fiat unit forshipment, and wherein the panels are relatively light and made of amaterial including an expanded clay, sand, and a binder.

Further objects and advantages of the present invention will be apparentto those skilled in the art to which it relates from the followingdetailed description of the preferred embodiment thereof made withreference to the accompanying drawings forming a part of thisspecification and in which:

FIG. 1 is a view, partly in elevation and partly in section of a hot topembodying the present invention and shown mounted in the open upper endof an ingot mold;

FIG. 2 is a plan view of a structure forming a part of the hot top shownin FIG. 1 prior to assembly thereof in the hot top;

FIG. 3 is a cross-sectional view of a hot top of a modified constructionand embodying the present invention and shown mounted in the upper endof an ingot mold; and

FIG. 4 is a graph illustrating a characteristic of the material of whichparts of the hot tops of FIGS. 1 and 3 are made.

The preferred embodiment of the present invention is illustrated in FIG.1 which shows a hot top supported in the upper end of an ingot mold 11.The hot top 10 has a central opening 10a therethroug-h through whichmolten metal is poured into the ingot mold, and the hot top maintains amass of mloten metal above the ingot to feed the shrinkage cavity as theingot cools, as is well known. The hot top 10 is herein shown as beingsimilar in construction to the hot top disclosed in US. copendingapplication, Ser. No. 398,629 owned by the assignee of the presentinvention.

The hot top 10 includes a metal casing 12 which is conventional inconstruction and includes an upper section 13 and a lower section 14,which are suitably secured together. The upper section 13 of the metalcasing is provided at its upper end with an integral inwardly extendingcanopy or flange 15. The lower section 14 of the metal casing has at itslower end an integral inwardly extending lip or flange 16, which is ofless inward extent than the flange 15.

In the illustrated hot top, the metal casing 12 is lined with aninsulating material 17. The insulating material may take many forms,and, for example, may comprise a porous fragile, relatively goodinsulating brick having low thermal conductivity and low heat capacityand weighing approximately 55 pounds per cubic foot and having a rateduse temperature of 2600 F. The equivalent insulating castable may besubstituted for the above insulating brick.

This porous, fragile insulating brick or castable, if used to form thelining 17, has a maximum rated use temperature such that the lining 17would be destroyed or severely damaged by the thermal shock of directcontact with molten steel so that it would have to be replaced aftereach pouring operation. The destruction or damaging of the lining 17would be increased because of the mechanical abuses to which it. wouldbe subjected during the stripping of the hot top from the sink-headafter the ingot has solidified. For both these thermal and mechanicaldamage reasons, a protective veneer must be used to protect such softinsulating brick in order to get repeated economical usage from such alining.

The lining 17 may also comprise a hard dense, highly refractoryfirebrick or the equivalent weight and temperature service castablerefractory which, because of its density and mass, has relatively highthermal conductivity and high heat capacity, and therefore relativelypoor insulating characteristics, but has good mechanical strength, andtherefore is easier to use and has a long economical life in a hot topbecause of its greater resistance to thermal shock and mechanicaldamage. Such a dense hot top lining, however, requires that a highermetal volume be poured to achieve metallurgical results equal to thoseobtained when more insulating brick linings are used, unless relativelylightweight, highly insulating, refractory panel means, as in thesubject invention, is used in combination with such hard dense linings17.

When dense brick or castable linings are used in combination with highlyinsulating refractory panels, equal metallurgical results can beobtained to those obtained with porous insulating brick linings, butwith the advantage of using hard brick or castable linings 17 which areeasier and more economical because of lower original cost and longerservice life. It is also possible with highly insulating refractorypanel means as in the present invention to use such panel means, when ofsuflicient thickness, directly against the cast iron casing or withlining 17 constructed of cast iron.

In the preferred embodiment, the insulating lining 17 is supportedbetween the flanges 1S and 16 and it is semipermanent in that it may beused for a number of pouring operations. The insulating lining 17 has aninner surface 17a which is tapered from the innermost end of the flange16 upwardly toward the flange 15 and no part of the lining 17 extendsinwardly beyond the flange 15. The lower end of the lining 17 does notextend inwardly of the hot top beyond the flange 16 and may be said tobe flush therewith, the advantages of which will be clear as thedescription proceeds.

Refractory panel means including panels 25, 26 are used to overlie thelining 17 to protect the lining. The insulating refractory panels can bevaried in insulating properties, as hereinafter described, for use withvarying hot top linings 17 of different thermal and mechanicalproperties, as above described. The more dense refractory panels areused with soft insulating brick linings and are primarily designed toprotect such brick from mechanical damage and thermal shock by providinga sulficient temperature drop or gradient between the temperature of themolten metal and the temperature to which the insulating lining 17 issubject so that the latter temperature is within the rated use of thelining. The lightening of such panels by additions of lightweightaggregate is primarily to facilitate handling of larger size panels.

Lighter, highly insulating refractory panels are designed primarily toprovide in the insulating panels themselves all or almost all of theinsulation required to produce a hot top sinkhead of the relatively lowmetal volume desired and required in the particular ingot castingoperation. The insulating lining 17, whether light and insulating ormore dense, is protected by such panel means and as a result, the lining17 is a semi-permanent lining capable of being reused for a number ofpouring operations.

In preparing the hot top for a pouring operation, the hot top is placedin a suitable stand in an inverted position, as is well understood inthe art. The protective panel means in the form of a preformed panelinsert unit 23 is then inserted into the interior of the hot top andplaced in position in contact with the insulating lining 17. The insertunit 23 forms an annular protective layer around the interior of the hottop and protects the lining 17 from thermal shock.

The preformed insert unit 23, as shown in FIG. 2, for protecting thelining 17 comprises a plurality of the individual panels 25, 26 suitablysecured to a flexible means or material 27. The panels 25, 26 form sideand corner panels, respectively, and are secured to the flexiblematerial 27 in any suitable manner, for example, by adhesives ormechanical means, such as rivets, pins, or clips. Alternatively, thepanels may be molded and formed directly on the flexible material duringthe manufacture of the units.

The flexible means 27 preferably is corrugated cardboard. However, it isto be understood that any flexible material which has suflicientstrength to support the inserts 25, 26 could be used, for example,cloth, cardboard strips, paper, fibrous material or pressure-sensitivetape may also be used. Moreover, a reinforcing wire screen may be usedas a flexible means and may be embedded in the panels 25, 26.

The panels 25, 26 are supported by the flexible material and, in thepreferred embodiment, on the cardboard sheet 27 in such a way that theannular edges 40a, 41a, respectively, of the panels are parallel and asmall spacing 45 is provided between each of the panels. The spacing 45is such that the insert unit 23 may be easily folded by grasping theopposite ends of the insert unit 23 and folding the flexible materialalong a line in the space 45 between the panels to an angle necessary tobring the adjacent edges of the panels into engagement. The positioningof the panels 25, 26 is such that when the flexible material is folded,the edges of the panels properly mate with a surface area contact andform a hollow geometric figure. During the preparation of the hot topfor the pouring operation, the insert unit 23 is placed in the hot top,as noted above. Specifically, the hollow geometric figure formed by theinsert unit is positioned over the inverted hot top and pushed intoposition.

In the illustrated embodiment, the cardboard material 27 does notcompletely overlie the panel inserts 2-5, 26. A small portion 30 of thepanel inserts extends beyond the cardboard at one edge 27a thereof,while a portion 31 of the panels 25, 26 extends beyond the cardboard atthe other edge 26b thereof. The portion 30 of the panel inserts extendsso as to overlie the inner surface a of the flange 15 so that theleakage of molten metal between the flange 15 and the insert unit 23 isminimized and thereby flow of the molten metal into contact with thelining 17 which would cause damage thereto is minimized.

The edge 27a of the cardboard which is adjacent to portion 30 functionsas a stop means for assisting in properly positioning the insert 23 inthe hot top. The edge 27a engages a tapered surface portion 33 of theflange 15 when the insert 23 is inserted into the hot top. Thus, theinsert unit is pushed into the hot top and stopped by the engagement ofthe cardboard with the tapered surface portion 33, whereby the insertpanels 25, 26 are properly positioned and do not extend beyond the upperend of the hot top. Because of the tapered opening and thecompressibility of the cardboard, the insert unit may be forced into thehot top in a manner that the adjacent edges 40a, 41a of the panels 25,26 properly meet, minimizing the possibility of leakage therebetween. Bycompressing the cardboard when the insert 23 is pushed into position,the contacting surface areas at the adjacent edges of the panels 25, 26are held in tight contact.

The portion 31 of the panels 25, 26 is received in a recess 36 in abottom ring member 37 positioned on the bottom of the hot top.Positioning of the portion 31 of the inserts in the recess 36 minimizesleakage of the molten metal into the area behind the insert where itmight contact and damage the lining 17. Moreover, by constructing thelining 17 so as to have its lower end flush with the flange 16, contactof the molten metal with the lining 17 is even further minimized, forthe flange 16 has a surface area contact with the insert 23 at alocation between the lining 17, on the one hand, and the abutting end ofthe portion 31 and the recess of the bottom ring, on the other hand.Moreover, the bottom end of the insert 23 bears against the inner end ofthe flange 16 which supports the bottom end of the insert so that itdoes not move outwardly upon pouring of the molten metal, which outwardmovement would result in an opening up of the area between the adjacentedges 40a, 41a of the panels 25, 26 and cause leakage therebetween. Theflange 15 against which the upper end of the insert units bear providesa similar support for the upper end of the insert 23.

The bottom ring 37, of course, may be secured on the hot top casing inany conventional manner and a wiper strip 38 is also attached to the hottop and forms a portion thereof. The details of the bottom ring 37 areknown in the art and will not be described. The wiper strip and bottomring, of course, function in the usual and conventional manner.

It should be noted that since the central opening 10a of the hot top istapered, the insert unit 23 when manufactured, that is, when in its flatcondition, as illustrated in FIG. 2, is segmented and somewhat curved,and when folded, forms a trapezoidal shape. Moreover, the panels 25, 26are tapered and the narrow ends of the panels overlie the surface 15a ofthe flange 15, as described hereinabove. The particular shape of thepanels and the insert unit 23, of course, will vary depending upon theshape of the hot top in which they are used and whether or not theopening in the hot top is tapered.

According to the present invention, the refractory panels 25, 26 aremade of a refractory insulating material which renders the panelsextremely light in weight and gives the panels good insulating andthermal properties which make the panels 25, 26 extremely effective foruse in a hot top. Moreover, the light weight of the panels provides foreasy handling of the panels. The material of which the panels 25, 26 aremade includes a lightweight cellular material, commonly referred to asexpanded clay. The expanded clay may be in the form of unicellular ormulticellular substantially rounded grains or bodies. The expanded clayis formed, as is known, in a fusing process wherein natural clay iscaused to be bloated or formed into a cellular substantially roundedgrains in a suitable furnace, as noted hereinabove. This granularmaterial is marketed under the trademark SCR Veri-lite and has a densityof approximately 25-35 lbs. per cu. ft.

The material of which the panels are made preferably also includes asand and a binder. The binder may be of any conventional form and maycomprise a synthetic resin, silicone resin, or an organic resin.Preferably, a resin binder and a cereal binder, a well-known binder inthe refractory art, are utilized in combination as the binder. Inpreparing the material of which the panels are made, the sand, expandedclay, and binder are mixed together in a conventional manner in asuitable vessel, such as a well-known muller and in the desiredproportions, as set forth hereinbelow. A suitable amount of water isadded to the mixture to facilitate the mixing and molding of thematerial. After the ingredients are thoroughly mixed, the panels aremolded in a conventional manner and dried. A small percentage ofkerosene may be added to the mixture to facilitate molding thereof.

The proportions of the various ingredients of the material of which therefractory panels 25, 26 are made may vary considerably. The expandedclay is an extremely good insulator and is extremely light in weight andas the percentage of the expanded clay increases in the mixture, theinsulating properties of the panel made of the material are increasedand the thermal efficiency of the hot top is increased. Moreover, theweight of the panel is decreased providing an extremely light weightpanel. However, as the percentage of the expanded clay in the mixtureincreases, the panels lose mechanical strength. On the other hand, asthe percentage of the expanded clay decreases in the mix, the insulatingproperties of the panels are impaired and the weight of the panels isincreased. However, the strength of the panels is also increased.

Table I, below, indicates various mixes which have been prepared andfrom which hot top panels have been made and the manufacturing range foreach ingredient which provides highly acceptable panels.

TABLE I MIX (parts by weight) Ingredient Manufacturing range KeroseneTable II, below, indicates the various ingredients which comprise thematerial forming the completed panels after drying of the molded panelswith the manufacturing range of parts by weight of the ingredients inthe panels.

TABLE II Ingredient: Range (parts by Weight) Expanded clay 15-85 Sand15-85 Cereal binder -6 Resin binder 3-10 It should be noted that thewater and kerosene added to the mix are not found in the final productsince they are removed therefrom through the drying process.

While the manufacturing range of expanded clay as shown in Table II isfrom 15-85 parts by weight, for certain uses, the amount of expandedclay may be as much as 90 or 95 parts by weight with the remainderbinder and without any sand at all in the panel, which would provide anextremely lightweight and highly insulating panel of rather poormechanical strength. On the other hand, the amount of expanded clay inthe product may be as little as parts by weight which would provide apanel insert having slightly improved insulating properties over thatwhich utilizes sand only, and of good mechanical strength. It should beapparent from the above that the specific proportions of sand, clay, andbinder may be selected to provide a panel with the properties requiredfor the desired use.

In hot tops utilizing a porous, fragile insulating brick of relativelygood insulating properties for the lining 17, the percentage of expandedclay in the protective panels may be relatively low, since in such acase the lining 17 would provide the major insulation. In hot topsutilizing the high grade, hard dense brick, of relatively poorinsulating properties, the percentage of expanded clay may be higher inorder for the protective panel to provide the major insulation requiredfor the molten metal. Thus, it can be seen that as the properties of thelining 17 vary, the percentage of the expanded clay in the panels mayvary to provide for best results.

When the panels mounted on flexible material, such as shown in FIG. 2,are to be used in connection with a hard castable lining, such as onehaving a density of 120-140 lbs. per cu. ft., the density of the panelsshould be in the range of approximately 30 lbs. per cu. ft. to 60 lbs.per cu. ft. The panels should have a minimum modulus of rupture of about250 lbs. per sq. inch. The panels would also have a thickness range ofbetween 1" and 2". The mixes Afl) stated above are of these approximaterange limits. That is mix D provides a panel having a density of about30 lbs. per cu. ft., while mix A above provides a panel having a densityof approximately 60 lbs. per cu. ft. Therefore, the mixes A and Drepresent the extremes for the range of materials used in making panelsfor use in connection with hard castable or on cast iron. A more narrowand preferred range is the range between mixes A and C.

The grain size of the expanded clay is quite large with more than 90percent of the expanded clay having a grain size larger than 30 U.S.mesh. The sand utilized in the mixture with the expanded clay preferablyis a coarse sand, known in the art as 40/ 60 sand, and has a grain sizesuch that 90 percent thereof has a grain size greater than 70 U.S. mesh.Of course, depending upon the amount of expanded clay in the mixture,the type of sand and grain size of the sand utilized may vary. More than90 percent of the mix of sand and expanded clay in the preferred rangeshas a grain size greater than 140 U.S. mesh, and preferably 20-80% ofthe mix has a grain size greater than 30 mesh.

The bar graph of FIG. 4 shows the grain size of the expanded clay and ofthe 40/60 sand and of the mixture of the 40/ 60 sand and expanded clayfor a mix having equal weights of sand and expanded clay, that is, mixB, as shown in Table I above. The legend accompanying the bar graphindicates which bars designate the mix, sand, and expanded clay. Itshould be apparent from the graph that the largest percentage of the mixhas a grain size within the range of greater than 30 U.S. mesh and lessthan 20 U.S. mesh and the percentage of the mix at other grain sizesdecreases as the grain size increases and decreases from the grain sizeof the largest percentage of the mix.

The panels formed from the material disclosed hereinabove are moldedinto the desired shape and thickness for the particular insert or hottop in which they are to be used and are dried into self-sustainingseparate panels having substantially parallel faces. The panels, ofcourse, include the expanded clay bonded together with sand and thebinder in a unitary structure with the cells of the expanded clayproviding the desired porosity in the panel. When the panels made of theabove-disclosed material are inserted into the hot top, the molten metalcontacts the panels causing the panels to waeaken and readily collapse,which is a desirable property in hot top insulating panels, and permitseasy cleaning of the lining 17 of the hot top and stripping of the hottop from the ingot. Moreover, the material including the expanded claywill not soften at temperatures normally encountered in connection withmolten steel. Thus, the material is capable of withstanding extremelyhigh temperatures without fusing and has substantial insulatingproperties, as well as permitting easy handling of the panel.

Panels made of the material disclosed above may be used in any type ofhot top, and FIG. 3 illustrates a modified form of hot top structure inwhich panels made of the material disclosed above are embodied. In FIG.3, the hot top is comprised of a plurality of panels 70 of theinsulating material which are suitably connected together in aconventional way to form a hot top and which are supported at the upperend of an ingot mold by a plurality of hot top supporting hooks 71. Thepanels which comprise the hot top may be formed of the materialdisclosed hereinabove and, in effect, provide a one-use hot top.

The refractory material or composition disclosed hereinabove may be usedin numerous ways in hot top structures and the modifications shown inFIGS. 1 and 3 are merely two illustrated ways of utilizing the materialin a hot top structure. The mixture disclosed hereinabove or thecomposition disclosed hereinabove may be utilized with or in conjunctionwith multilayer inserts or hot top panels wherein the layer of the panelwhich is to engage the molten metal is made of an exothermic material,as is well known, and which may be mounted on or bonded to a layer ofthe material disclosed hereinabove, or where the material disclosedhereinabove is bonded or connected to various other materials whichfunction as backings for the material disclosed above.

It should be apparent that the preferred embodiment of the presentinvention has been described in considerable detail and it is to beunderstood that the invention is not limited thereto but is to beconstrued as including all variations thereof which are covered by theappended claims.

Having described our invention, we claim:

1. A panel insert unit for use in hot topping, said unit having a frontside and a rear side remote therefrom and comprising a plurality of heatdestructible panel sections having front faces for forming adjacentinterior faces of a hot top opening, said panel sections having a sideelge surface facing each adjacent panel section with the side edgesurfaces each being in a plane defining an obtuse included angle withthe front face of the panel section, material extending between andinterconnecting said panel sections adjacent the rear side of the unitand providing for relative angular movement of said panel sections froman opened-out shipping position where facing edge surfaces of adjacentpanel sections are spaced to a position where the spaced edge surfacesof adjacent panels are in substantial contact to position the panels toform interior faces of the hot top and to block leakage of molten metalbetween the panels, said panels being made of a material including acellular granular expanded clay material having a density ofapproximately 25 to 35 lbs. per cu. ft., said panels having a densitybetween about 30 and 90 lbs. per cu. ft, a modulus of rupture ofapproximately 250 lbs. per sq. inch and a thickness of between 1" and2".

2. A panel insert unit as defined in claim 1 wherein said panels haveproperties of heat capacity and thermal conductivity approximatelyequivalent to an insulating firebrick panel of the equivalent densityand thickness.

3. A panel insert unit for use in hot topping, said unit having a frontside and a rear side remote therefrom and comprising a plurality of heatdestructible panel sections having front faces for forming adjacentinterior faces of a hot top opening, said panel sections having a sideedge surface facing each adjacent panel section with the side edgesurface of each being in a plane defining an obtuse included angle withthe front face of the panel section, material extending between andinterconnecting said panel sections adjacent the rear side of the unitand providing for relative angular movement of said panel sections froman opened-out shipping position where facing edge surfaces of adjacentpanel sections are spaced to a position where the spaced edge surfacesof adjacent panels are in substantial contact to position the panels toform interior faces of the hot top and to block leakage of molten metalbetween the panels, said panels being made of a material including to 85parts by weight of a cellular granular clay material having a densityapproximately 25 to 35 lbs. per cu. ft., 15 to 85 parts by weight ofsand, and a binder including 0 to 6 parts by weight of a cereal binderand 3 to parts by weight of a resin binder.

4. A panel insert unit for use in hot topping, said unit having a frontside and a rear side remote therefrom and comprising a plurality of heatdestructible panel sections having front faces for forming adjacentinterior faces of a hot top opening, said panel sections having a sideedge surface facing each adjacent panel section with the side edgesurfaces each being in a plane defining an obtuse included angle withthe front face of the panel section, material extending between andinterconnecting said panel sections adjacent the rear side of the unitand providing for relative angular movement of said panel sections froman opened-out shipping position where facing edge surfaces of adjacentpanel sections are spaced to a position where the spaced edge surfacesof adjacent panels are in substantial contact to position the panels toform interior faces of the hot top and to block leakage of molten metalbetween the panels, said panel sections being made of a materialincluding at least 40 parts by weight of expanded clay having -a densityof approximately 25-35 pounds per cubic foot, at least 40 parts byweight of sand, and at least 3 parts by weight of a heat collapsiblebinder.

5. A panel insert unit as defined in claim 4 wherein said materialfurther includes at most 6 parts by weight of a cereal binder.

6. A panel insert unit for use in hot topping, said unit having a frontside and a rear side remote therefrom and comprising a plurality of heatdestructible panel sections having front faces for forming adjacentinterior faces of a hot top opening, said panel sections having a sideedge surface facing each adjacent panel section, material extendingbetween and interconnecting said panel sections adjacent the rear sideof the unit and providing for relative angular movement of said panelsections from an opened-out shipping position where facing edge surfacesof adjacent panels sections are spaced to a position where the spacededge surfaces of adjacent panels are in substantial contact to positionthe panels to form interior faces of the hot top and to block leakage ofmolten metal between the panels, said panels being made of a materialincluding 15 to parts by weight of a cellular granular clay materialhaving a density approximately 25 to 35 lbs. per cu. ft., 15 to 85 partsby weight of sand, and a binder including 0 to 6 parts by weight of acereal binder and 3 to 20 parts by weight of a resin binder.

References Cited UNITED STATES PATENTS 85,340 12/1868 Smith 106-3891,778,316 10/1930 Forrest 249-201 1,984,759 12/1934 Patton 106-3892,856,657 10/1958 Urmetz 249-204 X 3,171,173 3/1965 Ingala 249-623,221,382 12/1965 Haw 249-201 I. SPENCER OVERHOLSER, Primary Examiner.

EUGENE MAR, Assistant Examiner.

US. Cl. X.R.

